In order to control the silicon deoxidation reaction for steel including molybdenum, it is necessary to take into account the thermodynamic affinity of molybdenum with silicon. For the calculation of the deoxidation equilibria in the alloyed steel including molybdenum, it is necessary to know the interaction parameter of molybdenum for silicon. However, it is difficult to explain the silicon deoxidation of the alloyed steel including molybdenum by previously reported thermodynamic data. Accordingly, the equilibrium for silicon distribution between Fe and Ag phases in Fe–Ag–Si–Mo system and the deoxidation equilibrium of molten Fe–Mo alloy with silicon are investigated at 1873 K. The atomic fraction interaction parameter of Mo for Si, εSi (in Fe)Mo, is determined to be 43(±13) from the equilibrium for silicon distribution between Fe and Ag phases in Fe–Ag–Si–Mo system. The experimental results on the deoxidation equilibrium of molten Fe–Mo alloy with silicon reasonably agree with the calculated ones by using εSi (in Fe)Mo=43(±13) derived in the present study. The oxygen contents after the deoxidation treatment by silicon are estimated for 8 kinds of steel. The oxygen content of ferrous alloys including molybdenum can be reasonably estimated using the interaction parameter of Mo for Si derived in the present study.
The clarification of chlorides evaporation behavior from chloride or oxychloride melts is quite important for the treatment and recycling of fly ash generated from incineration processes of municipal solid waste. In the present study, the evaporation rate of the molten PbCl2–ZnCl2 binary chloride system was measured at 973, 1023 and 1073 K. The effects of temperature, composition of the melt and the oxygen partial pressure of atmosphere on the evaporation rate of molten chloride were investigated. The ZnCl2 in chloride melt evaporated preferentially, but the evaporated amount of PbCl2 was negligibly small. Calculated activation energy of ZnCl2 evaporation was 194±4 kJ/mol and that evaporation rate was smaller than that estimated from ZnCl2 activity for the PbCl2–ZnCl2 system. Therefore, the evaporation is considered to be controlled by the slower chemical reaction step than the interfacial evaporation reaction. The evaporation rate increased with increasing oxygen partial pressure in the atmosphere, which might be due to the effect of oxychloride formation.
The integrated blast furnace and oxygen steelmaking (BF-OSM) route is still a dominant process for worldwide steel production, currently producing more than 60% of the world's total output of crude steel. The counter-current principle on which the blast furnace operates makes it reliant heavily on the quality of its burden to maintain a sufficient level of gas permeability in its upper shaft and of liquid and gas permeability in its lower part. Iron ore sinter, constituting a major proportion of blast furnace burden in most countries, particularly in the Asia-Pacific region, is therefore expected to have a significant impact on blast furnace performance. The chemical composition of iron ore fines, together with the thermal conditions that sinter blends are subjected to, plays an important role in forming the primary melt during the sintering process and consequently determines the sinter structure and quality. Considerable emphasis has therefore been placed on the chemical composition and consistency of iron ore fines, particularly in terms of alumina content. However, due to the limited reserves and increasing depletion of high-grade iron ore resources, the alumina content of iron ores is expected to increase gradually. While the increase in such constituents is relatively slow over a long period, it has still caused problems for blast furnace operators. This paper attempts to clarify the role of different types of alumina present in iron ore fines and their effects on melt formation, sinter structure and sinter quality, as well as the sintering process itself. Mechanisms responsible for the deterioration of the low temperature reduction degradation characteristics (RDI) of sinter due to the increasing alumina content are also reviewed. In addition, potential measures to counter the adverse impacts of alumina on sintering performance of hematite iron ore fines are also discussed.
Pure Fe2O3 and Fe2O3 doped with either 2, 4, or 6 mass% MnO2 annealed at 1473 K for 6 h were isothermally reduced with carbon monoxide at 1073–1373 K. The oxygen weight loss resulted from the reduction at a given temperature was continuously recorded as a function of time. Reflected and scanning electron microscopes were used to characterize the annealed and reduced samples whereas the different phases developed were identified by X-ray phase analysis technique. The external volume of partially and completely reduced samples was measured by displacement method and the volume change (ΔV%) was calculated. At a given temperature, the influence of MnO2 mass% on the reduction behaviour and volume change of Fe2O3 compacts was investigated. The doping of MnO2 showed different effects during the reduction of Fe2O3 which is temperature dependant. At <1198 K, the rate of reduction decreased at early stages with the increase in MnO2 mass% due to the presence of hardly reducible manganese ferrite phase (MnFe2O4). At final reduction stages the retardation effect was attributed to the formation of dense iron manganese oxide (FeO0.899, MnO0.101). At ≥1198 K, the presence of MnO2 promoted the reduction of Fe2O3 and the catastrophic swelling resulted from the formation of both metallic iron plates and whiskers was observed. Maximum swelling (ΔV%) was measured at 1198 and at 1248 K for pure Fe2O3 and MnO2-doped compacts respectively and it increased with the increase in MnO2 mass% resulting about 405% for 6 mass% MnO2-doped samples. The reduction mechanism was predicted from the correlation between the apparent activation energy values, testing of different mathematical formulations derived from gas-solid reaction model and the microscopic examination of partially reduced compacts.
Rapid in-flight reduction of fine iron ore transported with CO, H2 and/or CH4 gas has been studied for direct use of fine iron ore in iron-making process. In this work, the mechanism and the kinetic of the reduction by CH4 gas were accurately investigated with spherical wüstite fine particles. The spherical wüstite fine particle as fine iron ore was prepared to simplify the reduction rate analysis. Reduction temperature was varied from 1373 to 1573 K. As the result, fractional reduction of spherical wüstite by CH4 gas reached over 80% at 1573 K within 1 s. From the cross section observation of the particle after reduction, it was found that the periphery of the wüstite particle was metallized by reducing reaction and un-reacted wüstite core remained inside. Therefore, it was indicated that the reduction progressed topochemically in this experimental condition. In the reduction rate analysis, it was found out that the reduction rate by CH4 was higher than that by H2 or CO. From the carbon concentration analysis, it was found that the phase of the metallic shell during reduction was not only solid state but also liquid state. From the above-mentioned kinetic analysis, it was concluded that the reduction rate determining-step by CH4 was chemical reaction on Fe–FeO interface and the reduction of wüstite was preceded by the carbon dissolved into metallic shell from CH4 gas.
Exogenous non metallic inclusions can be introduced into steel from many external sources. Typical examples are the particles of refractory material which detach from their parent material during ladle treatment, teeming and casting operations, remaining entrained in the steel. In the present work, the interactions between Al2O3–SiO2 refractories and steel during casting of ingots has been deeply investigated, permitting to explain the occurrence of ghelenite- and grossite-types inclusions into special grade steels. The experimental analyses were carried out on non-metallic inclusions and ex-service refractory materials by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Microdiffraction (μXRD). The results were confirmed by thermodynamical considerations.
Synthetic V-bearing steelmaking slag modified by Al2O3, containing three different amounts of P2O5, were heated to 1530°C and then slow cooling to 1300°C for several durations. The effect of P2O5 on the solidified slags, especially on the crystallization behaviour of V-concentraitng phase were characterized by XRD, SEM and EPMA. The results show that V is concentrated and formed into Ca3(VO4)2 in P2O5-free slag and for the samples with 1.0 wt% and 2.4 wt% P2O5, V is precipitated into a solid solution Ca3[(P, V)O4]2. Ca3(VO4)2 and Ca3[(P, V)O4]2 are both the V-concentrating phases in the modified slag. Quantitative description of the morphologic texture of grains of the V-concentrating phases was based on computer-aided image analysis. For all samples, the fitted lognormal distribution is in good agreement with the distribution in the whole grain size range. It is concluded that P2O5 accelerates the growth of V-concentrating phase and influence the morphology of V-concentrating phase and growth mechanism is surface-controlled. There exists a proper content range of P2O5 between 1–2.4% for better growth of V-concentrating phase.
The mass transfer characteristics between liquid steel and powder particles in RH-PB(IJ) refining process have been investigated on a water model of 1/4 linear scale for a 150 t multifunction RH degasser. Sodium chloride powder with analytical purity has been utilized as the flux for injection. The mass transfer coefficient (k) of solute (NaCl) in the liquid has been determined under the conditions of the RH-PB(IJ) process. The effects of the main technological and structural parameters on the characteristics have been examined. It may be concluded from the results that, under the conditions of the present work, the mass transfer coefficient in the liquid increases with increasing the lifting gas flow rate, with increasing the inner diameter of the upsnorkel, with increasing the circulation rate of the liquid, and with increasing the particle size of powdered flux, and decreases with an increase in the inner diameter of the downsnorkel. Its value is in the range of (3.392×10−5–2.661×10−4) m/s. The corresponding dimensionless relationships for the mass transfer coefficient in the range were obtained. Taking the relative velocity of the particles to the liquid into account, the mass transfer in the liquid may be characterized by Sh=2+0.0285(Res)3/4Sc1/3 Considering the energy dissipation caused by the fluctuation in the velocity of the liquid in turbulent flow, the following dimensionless relationship has been reached: Sh=2+0.0285(εsldp4/vl3)1/4Sc1/3 When the mass transfer is regarded as that between rigid bubbles and molten steel, it may be characterized by: Sh=2+0.00731[Res0.48Sc0.339(g1/3dp/D2/3)0.072]1.455 In comparison with the mass transfers coefficient in the molten steel between the powder particles and the liquid in RH-PTB process, that in the conditions of RH-PB(IJ) refining is smaller, being about 1/4–1/3 of the former, but the both have a similar feature and pattern.
A new simultaneous desulfurization and deoxidation process of molten steel with magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is proposed. The pellets composed of MgO and Al are charged into an immersion tube and the magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is injected directly into molten steel to react with the dissolved sulfur and oxygen in it. Effects of various operating parameters on desulfurization and deoxidation are discussed. In the case of the high initial oxygen concentration, deoxidation of molten steel proceeds preferentially, and desulfurization does not take place. When the oxygen concentration in the melt is low enough, desulfurization of molten steel with magnesium vapor can proceed. A higher initial sulfur concentration increases the desufurization ratio of molten steel. The sulfur concentration in the melt tends to be in equilibrium with the magnesium partial pressure in the Mg–Ar bubble rather than the dissolved magnesium concentration in the melt. Increasing pellet mass promoted desulfurization of molten steel. The maximum desulfurization ratio of molten steel can be obtained at a relatively low argon carrier gas flow rate. In both cases of the porous magnesia and the dense alumina immersion tubes with injecting holes, addition of lime onto the melt surface increases the desulfurization ratio. The desulfurization using the dense alumina tube is accompanied by resulfurization more significantly at the later stage than that using the porous magnesia tube.
A full scale water modeling experiment has been conducted to address the relationship between the instability of fluid flow and level fluctuation in the continuous thin slab casting mould with the particle image visualization. The results show that the internal fluid flow and level fluctuation are unsteady and periodical. The probabilities of fluctuated meniscus and moving circumfluence center position seem Possion distributions with the highest frequency near the average position. The circumfluence and meniscus profile are asymmetrical, and the phase difference of wave height and circumfluence center in the two sides of mould centerline is half period. The average meniscus profile, the highest and lowest meniscus positions are generally symmetry about the mould centerline, and the circumfluence center swings with a similar trace. The wave height mainly depends on the circumfluence center position along the mould height. The wave height has an inverse relation with the circumfluence center depth, and the wave height decreases with descending circumfluence.
Continuous casting of slab caster of Tata Steel has been simulated using a three dimensional mathematical model based on considerations of fluid flow, heat transfer and solidification for better understanding of the process. Liquid metal comes in the mould by bifurcated nozzle. The principal model equations are momentum and heat balances. In various zones, different standard boundary conditions have been used. In the mould region, Savage and Prichard expression for heat flux has been used. In the spray cooling zone, heat transfer coefficient for surface cooling of the slab has been calculated by knowing the water flow rate and nozzle configuration of plant. The turbulence in the molten metal has been modelled by the Realizable k–ε model. CFD software (Fluent) has been used for the solution of equations to predict the velocities in the molten pool of the slab, temperature of the entire volume of the slab, heat transfer coefficient in the mould region, heat flux in the spray and radiation region and shell thickness. The variables studied are different casting speed.
Cast planning is a practical problem frequently encountered in steel industry. Its task is to group charges into batches (casts) with respect to the similarities of steel-grade and dimensions between charges, taking account of the practical technique constraints on life-span of tundish. Effective cast planning can reduce the changeover cost of charges and enhance the productivity of continuous casters. The objective under our consideration is to minimize the total dissimilarity costs between the charges in the same casts, to minimize the number of casts and the number of unselected charges. A quadratic integer programming model with multiple objectives for this problem is formulated. It is NP-complete, and so an iterated local search (ILS) algorithm is developed for the problem. In this algorithm, cyclic transfer neighborhood is adopted, in which several charges are transferred among casts simultaneously as a manner of cycle. A new kick strategy is developed with the idea of assigning charges to different casts according to the dissimilarity costs between them and the casts' central charges identified by the current solution. Computational results using real data from an advanced iron & steel company in China indicate that the ILS algorithm provides optimal solutions for small instances, and better near-optimal solutions for larger instances compared with a linear solver, Lingo 8.0, used to solve the equivalent linear integer programming obtained by transforming the original model. Totally, 92.3% of the instances are solved to global optima by the ILS algorithm while it is possible that the other 9.7% instances also are solved to optimal, which indicates the efficiency of the algorithm. At the same time, the algorithm also provides better solutions than the ones obtained by the current system used in the company.
In order to clarify the influence of reaction conditions on the formation of iron oxyhydroxides and oxides obtained from hydroxysulfate green rust (GR), the X-ray diffraction method was used for analyzing the solid particles formed during conversion. GR was synthesized from solutions of ferric sulfate, ferrous sulfate, and sodium hydroxide. The suspension containing GR was oxidized by passing oxygen gas. X-ray absorption spectroscopy and transmission electron microscopy were used for analyzing the chemical state and structure of the solid particles separated from the suspension, respectively. The results revealed that GR was converted primarily to α-FeOOH, and γ-FeOOH and Fe3O4 were found to be partially formed during the conversion depending on the temperature and oxygen flow rate. Furthermore, the addition of manganese was shown to enhance the formation of Fe3O4. These results indicate that the formation of different structures of iron oxyhydroxides and oxides in an aqueous solution is sensitive to the reaction conditions.
The crack spacing distribution of the Fe–Zn intermetallic coating layer of tensile-strained galvannealed IF (Interstitial Free) and SPCC (Steel Plate Cold Commercial, Japanese Industrial Standard) steels under tensile applied strain at room temperature was studied. The experimental and analytical results revealed that the crack spacing decreases with increasing applied strain due to the increase in stress transfer efficiency and the cumulative probability–crack spacing curves at any applied strain of both samples lie in a unique curve when the crack spacing is normalized with respect to the average value at each applied tensile strain. Then, by combining these features, a comprehensive description method of the crack spacing distribution was proposed, in which the influences of the thickness of the coating layer, substrate material and applied strain are incorporated. With the proposed method, the measured change of the probability density–crack spacing curve with increasing applied strain was described well for both samples. Also with this method, the variation of the probability density–crack spacing relation as a function of applied strain was predicted for different thickness of the coating layer and substrate material. Based on these results, the influences of multiple cracking that takes place in advance of spalling of the coating layer on the non-uniform spalling and the influences of thickness of the coating layer and substrate material on the spalling behavior were discussed.
The price of nickel is maintaining high level due to the demand continuing to outstrip supply, therefore the stainless steel, which is the largest consumer of nickel, has been maintaining a high-price. In this review, the way of nickel saving by more than half and the comparison of properties between the nickel saving stainless steels and Type 304 were reviewed, and the problem caused by the use of the nickel saving stainless steels were discussed. Nickel saving stainless steels have the following 4 types; martensitic stainless steels, ferritic stainless steels, duplex stainless steels and Cr–Mn–Ni austenitic stainless steels. Nickel saving stainless steels have both superior and inferior points as compared to Type 304, however they have a large possibility of substitution for Type 304. Further expansion of the use of nickel saving stainless steels is expected if the properties required for the stainless steel are reconsidered for proper demands.
Effects of alloy addition on magnetic anisotropies in non-grain oriented electrical steels were investigated. Tin and antimony improved magnetic induction and iron loss but increased anisotropy of magnetic induction and lessened anisotropy of iron less. Texture effect was evaluated as texture factor expressing as a rate of sum of volume fractions of cube and Goss textures to volume fraction of γ fiber texture. Magnetic anisotropy of iron loss is inversely proportional to texture factor and magnetic induction were turned out proportional to texture factor.
The nitrogen content in solution in the extra-mild steel sheets used in automotive or packaging industry after the different steps of their processing plays an important role both on the formability of the sheets and on their ability for strain ageing. This is why, the aim of the present work is to determine the conditions of the chromium nitride formation in a cold-rolled ULC steel with 0.7% Cr. In order to simulate the precipitation which may occur during the coiling or during the recrystallization annealing of the sheets, the investigated steel was submitted to different thermal treatments at temperatures ranging from 600 to 850°C. Then, the nitrogen content remaining in solution was evaluated after having defined a specific procedure based on thermoelectric power (TEP) measurements and using the segregation of the nitrogen atoms in solution to the dislocations introduced in the steel by cold-rolling. It was shown that the maximum precipitation speed is obtained at 650°C and that the precipitation is considerably delayed when the steel was recrystallized before the treatment.
Performing the solution nitriding treatment under pressurized nitrogen gas atmosphere, the microstructure change and the relationship between the nitrogen gas pressure and the solute nitrogen content in Fe–Cr alloys were investigated. The microstructure of the ferritic Fe–Cr alloys changed to an austenitic structure by the pressurized solution nitriding treatment at 1473 and 1573 K. However, in the case that their martensite temperature did not decrease sufficiently lower than room temperature, martensitic transformation occurred during the cooling process. Examination of the interaction on nitrogen activity with the thermodynamic method confirmed that the deviation between the experimental and theoretical solute nitrogen contents in Fe–Cr alloys widened greatly in the high nitrogen region over 3 at% N because of the strong N–N interaction in austenite. The interaction parameter eN[N] between N atoms in austenite iron at 1473 K was obtained as 0.120. The temperature dependence of eN[N] is expressed as follows: eN[N]=217/T−0.0273
The effect of aluminum content during the annealing of interstitial free high strength steel (IF-HSS) containing Mn, P, Ti and Nb was investigated. The resulting mechanical properties were evaluated and recorded. The results showed that a super formable high strength IF steel with an r-value equal to or higher than 2.3 can be obtained by Al additions. One of the interesting observations of this investigation was the change of precipitation behavior with aluminum content. Aluminum has the effect of improving the formability, especially the drawability, of the IF-HSS when more than 0.10 wt% Al is added. Texture analysis showed that the ‹111›//ND fiber (γ-fiber) was intensified, and ‹110›//RD (α-fiber) was weakened, with an increase of aluminum content. These benefits appear to result from the change of precipitation behavior with the increase of aluminum content. It was confirmed thorough the SANS analysis that the size of the precipitates in the sample with higher aluminum content was larger and their number was much fewer than in the sample with lower aluminum content. It appears that the high aluminum in IF-HSS containing Mn, P, Ti and Nb strengthened the scavenging effect of Ti or Nb and thus purifies the iron matrix.
A stress-based ductile forming limit theory applicable to nonlinear strain paths is investigated with a 11% Cr steel which displays a highly anisotropic behavior in plastic deformation. The forming limit stress is evaluated by a theoretical method based on the M-K theory, and is also measured directly in some cases with nonlinear loading paths. The evaluated and measured stresses are compared with an experimentally-obtained forming limit stress diagram, where the stresses are converted from strains by Stoughton's method. The theoretically-evaluated limit stress corresponds not to the measured stress at the onset of fracture but to the stress at the onset of localized necking. The evaluated forming limit stress and experimentally-obtained localized necking stress demonstrate no dependency on strains paths, thus verifying the applicability of the theory to this particular material. The experimentally-obtained forming limit stress diagram was corrected using the above results, which has improved the discrepancies between the experimentally- and numerically-obtained forming limit stress.
The ductile forming limit in nonlinear strain paths which include out-of-plane forming such as rolling was investigated for a 11% Cr steel sheet. For strain paths with only a plane stress state, e.g., in-plane strain, the forming limit stress diagram (FLSD) has been proven to be effective, even if the paths are nonlinear. In this research, a method of extending the FLSD theory to strain paths which include out-of-plane strain is investigated experimentally and theoretically. An experimental procedure is used to measure directly the stresses at the onset of diffused and localized necking and at the onset of separation with rolling-stretching loading paths. Theoretically, an assumption is introduced to consider out-of-plane strain in the M-K theory. The experimental and theoretical results of the forming limit stress show good agreement. When large rolling strain is induced in first-stage loading paths, this research demonstrated that there are cases where the FLSD theory is not effective for predicting the ductile forming limit. Those cases are characterized by a stress state of the re-yielding point in the final loading stage. If the point is outside the FLSD curve, the forming limit stress is not on the FLSD curve but located near the subsequent yield surface. Thus, a modified FLSD curve can be defined by the lines connecting the outer line of the conventional FLSD curve and the subsequent yield surface of the loading path under consideration. With this extension, it is possible to demonstrate the applicability of the FLSD method to processes which include out-of-plane loading paths such as rolling.
Substance flow analysis of molybdenum associated with iron and steel flow has been conducted in this study. The demand of molybdenum in iron and steel section reaches approximately 85% of total molybdenum consumption in Japan. Total demand of special steel products in final commodity is 18.4×106 t (for domestic: 12.4×106 t), and that contains 14.3×103 Mo-t (for domestic: 9.6×103 Mo-t) of molybdenum in 2004 fy. In addition, crude steel for special steel (23.8×106 t) contains 18.5×103 Mo-t of molybdenum. Approximately 70% (12.3×103 Mo-t) of molybdenum in the crude steel flows into domestic market, and about 45% of that is used for motor vehicles production. Improvement of dismantling technology and standardizing of special steel scrap will help to promote rare metal recycling.